1. Field of the Invention
The present invention relates to a semiconductor device including a metal oxide semiconductor field effect transistor (MOSFET), and a protection circuit for protecting the MOSFET from being subjected to a breakdown.
2. Description of the Related Art
In such a semiconductor device, a MOSFET may be used as a power ON/OFF switch to energize and de-energize a load circuit containing an inductor. Namely, when the MOSFET is turned ON, the load circuit is energized. When the MOSFET is turned OFF, the load circuit is de-energized. When the load circuit is de-energized, a counter electromotive force is generated by the inductor of the load circuit. At this time, a voltage is applied to the drain of the power MOSFET device due to the generation of the counter electromotive force. When the applied voltage is too large, the power MOSFET device may be subjected to a breakdown.
JP-H08-172190 A has proposed a semiconductor device in which a protection circuit made of a plurality of Zener diodes is connected to a power MOSFET so that the power MOSFET may be protected from the breakdown, as discussed in detail hereinafter.